Of course location is not a guarantee of fast speeds, but you can at least check servers nearby with https://lemmy.fediverse.observer/map. I guess you can check for uptime to have an idea about reliability, but I never really relied on that. Shit happens (vlemmy comes to mind) so it’s hard to gauge an instance’s future reliability. You have the option to start your own instance as well.

https://github.com/CMahaff/lasim